Question

find the centre and radius of the circle x²+y²-8x-4y-5=0

Answer 1

this is the form of circle and it's equation is X^2+Y^2+2gX+2fY+c=0. so when we compare the equation to your equation here the centre is (-g,-f) and radious is √g^2+f^2-c. so the radious is √16+4+5=5 and centre is (4,2).